Chemokines are a family of about 50 small proteins that modulate cell trafficking and angiogenesis and also play a significant role in the tumor microenvironment (Vicari et al., 2002). Depending on their structure, chemokines are classified as C-C chemokines (containing a cysteine-cysteine motif) or C-X-C chemokines (containing a cysteine-X-cysteine motif). Receptors that bind such chemokines thus are classified as members of the CCR family or CXCR family, respectively.
One member of the CXCR family is the CXCR4 receptor (CXCR4), also known as CD184, a seven-transmembrane domain G-protein coupled receptor consisting of an extra-cellular N-terminal tail and three extra-cellular loops. The intracellular carboxy terminus of CXCR4 is coupled to a heterotrimeric G-protein consisting of β and γ subunits and a pertussis toxin-sensitive Gi α subunit (Loetscher et al., 1994). To date, only one ligand for CXCR4, a chemokine known as CXCL12 (also known, and used interchangeably herein, as stromal cell-derived factor-1 or SDF-1) has been identified (Bleul et al., 1996; Oberlin et al., 1996). CXCL12 binding to CXCR4 stimulates activation of phospholipase C and subsequently results in an elevation of cytosolic free calcium. Ligation of CXCR4 ultimately leads to induction of chemotaxis and migration (Tachibana et al., 1998; Zou et al., 1998). CXCR4 also plays a role in embryogenesis, homeostasis and inflammation. Studies with mice engineered to be deficient in CXCR4 or CXCL12 implicate the CXCR4/CXCL12 pathway in organ vascularization, as well as in the immune and hematopoietic systems (Tachibana et al., 1998). Further, CXCR4 has been shown to function as a coreceptor for T lymphotrophic HIV-1 isolates (Feng et al., 1996).
In healthy adults, CXCR4 is predominantly expressed on hematopoietic lineage cells including B and T cells, monocytes, macrophages, NK, and dendritic cells, as well as CD34+ bone marrow (BM) progenitor cells (Lee et al., 1999). Low levels of CXCR4 are also expressed on endothelial and epithelial cells, astrocytes, and neurons (Gupta et al., 1998; Hesselgesser et al., 1997). CXCL12 has been shown to induce endothelial cell migration and proliferation and, together with VEGF, has been shown to enhance neoangiogenesis (Guleng et al., 2005). Over-expression of CXCR4 has also been found in 75% of cancers including leukemias, lymphomas, pancreatic, breast, ovarian, lung, prostate and colorectal tumors, and the interaction between CXCL12 and is essential for homing and maintaining hematopoietic stem cells within the BM microenvironment (Mohle et al., 1998). Plerixafor (AMD3100; Mozobil), a bicyclam antagonist of CXCR4, has been shown to mobilize stem cells into the bloodstream (Dar et al., 2011). AMD3100 and AMD3465, another CXCR4 antagonist bicyclam, increase chemosensitization of AML tumor cells by blocking CXCR4/CXCL12 signaling (Nervi et al., 2009; Zeng et al., 2009).
AML is a fast-growing cancer of the myeloid line of blood cells, characterized by the rapid growth of abnormal white blood cells that accumulate in the BM and interfere with the production of normal blood cells. In AML, CXCR4 is highly expressed on the CD34+ fraction of BM cells. Lower levels of CXCR4 on AML cells correlate with a better prognosis resulting in a longer relapse free and overall survival. The lower CXCR4 receptor expression attenuates migration of primary AML cells toward CXCL12 expressed in the chemo-protected environment of the BM (Tavor et al., 2004).
Multiple myeloma (MM) is a form of cancer that results from the malignant proliferation of plasma cells. After non-Hodgkin's lymphoma, it is the second most frequent hematological cancer, with approximately 80,000 new cases worldwide (20,000 in the United States), and approximately 62,000 deaths per year (10,500 deaths/year in the U.S.) (Jemal et al., 2008; 2009). MM cells grow preferentially in the BM where they interfere with the production of normal blood cells and normal antibodies, resulting in immunodeficiency, skeletal destruction, hypocalcemia, BM and renal failure. In addition to AML, serum levels of CXCL12 are elevated in patients with MM, and CXCR4 expression increases in extramedullary plasmacytoma, a manifestation of an advanced stage of MM. Furthermore, blockade of the CXCL12/CXCR4 axis attenuates migration of MM cells and homing of these cells to the BM (Alsayed et al., 2007).
Non-Hodgkin lymphomas include any of a diverse group of cancers of lymphocytes other than Hodgkin's lymphomas. NHLs can occur at any age and are often marked by lymph nodes that are larger than normal, fever, and weight loss. The many different types of NHL vary significantly in their severity, from very aggressive (fast-growing) to indolent (slow-growing) types, and they can be formed from either B-cells or T-cells. B-cell NHLs include Burkitt's lymphoma, chronic lymphocytic leukemia/small lymphoid lymphoma (CLL/SLL), diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), immunoblastic large cell lymphoma, precursor B-lymphoblastic lymphoma, and mantle cell lymphoma. T-cell NHLs include mycosis fungoides, anaplastic large cell lymphoma, and precursor T-lymphoblastic lymphoma. It is estimated that there will be approximately 70,000 new cases of NHLs in the United States in 2012, which will result in about 19,000 deaths. High-level CXCR4 expression has been demonstrated in 18 out of 19 primary NHL cell lines tested (Bertolini et al., 2002). It has also been shown that CXCL12 enhances migration of follicular NHL cells (Corcione et al., 2000), and the CXCR4-CXCL12 circuitry appears to be crucial for migration of CLL cells (Burger et al., 1999).
Human anti-CXCR4 monoclonal antibodies that exhibit numerous desirable properties have previously been described in PCT International Publication No. WO 2008/060367 (Application No. PCT/US2007/021152), claiming priority to U.S. Provisional Application No. 60/827,851, filed Oct. 2, 2006. The disclosures of both these applications are hereby incorporated in their entireties by reference into this application. As disclosed in WO 2008/060367, in vitro studies demonstrate that these monoclonal antibodies bind to CXCR4-expressing cells with low nanomolar affinity, block CXCL12 binding to CXCR4-expressing cells, and inhibit CXCL12-induced migration and calcium flux with low nanomolar EC50 values. One of the fully human monoclonal antibodies, BMS-936564, (designated F7 in WO 2008/060367, previously designated MDX-1338, and also assigned the non-proprietary name, ulocuplumab, by the United States Adopted Names (USAN) Council, all four designations being used interchangeably herein), which exhibited unexpectedly advantageous anti-solid tumor properties in preclinical studies, has been selected for further investigation to determine its activity against hematologic cancers in vivo and to further elucidate the mechanisms underlying its anti-cancer activity. Ulocuplumab (BMS-936564) has also entered Phase I clinical studies in patients with relapsed/refractory AML, MM, and NHLs.